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The information in this web site is an update of the Route Log and Finder List for the Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate System. This provides a simple means for locating routes by number or to find which routes serve each State and its larger cities and major metropolitan areas. It shows the total mileage of each route in each State and includes those that were constructed with the aid of Federal funds and those that were added per the States' requests and approved by the Federal Highway Administrator as logical additions or connections to the Interstate System after upgrading to Interstate design and construction standards (except for Alaska and Puerto Rico).
The Route Log and Finder List is composed of a brief discussion of the history of the Interstate System, how the routes and interchanges are numbered, the status of the System As of December 31, 2016, and other relevant information about the System, and four Tables, as follows:
The origins of what is now called the Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate System, are a series of studies on the need for transcontinental highways. The Federal-Aid Highway Act of 1938 called on the Bureau of Public Roads (BPR), the predecessor of the Federal Highway Administration (FHWA), to study the feasibility of a toll-financed system of three east-west and three north-south superhighways. The BPR's report, Toll Roads and Free Roads, demonstrated that a toll network would not be self-supporting. Instead, the report advocated a 26,700-mile toll-free interregional highway network.
In 1941, President Franklin D. Roosevelt appointed a National Interregional Highway Committee, headed by Commissioner of Public Roads Thomas H. MacDonald, to evaluate the need for a national expressway system. The Committee's January 1944 report, Interregional Highways, supported a system of 33,900 miles of rural routes, plus an additional 5,000 miles of auxiliary urban routes.
Congress acted on these recommendations in the Federal-Aid Highway Act of 1944. The Act called for designation of a National System of Interstate Highways, to include up to 40, 000 miles " ..... so located, as to connect by routes, direct as practical, the principal metropolitan areas, cities, and industrial centers, to serve the National Defense, and to connect at suitable border points, routes of continental importance in the Dominion of Canada and the Republic of Mexico."
On August 2, 1947, Commissioner Thomas H. MacDonald and Federal Works Administrator Philip B. Fleming announced selection of the first 37,700 miles. The routes had been proposed by the State highway agencies and reviewed by the Department of Defense. However, neither the 1944 Act nor later legislation in the 1940's authorized funds specifically for the Interstate System. The lack of funding hindered plans for the System's construction.
Funding for the System was first authorized in the Federal-Aid Highway Act of 1952, but it was only a token amount of $25 million a year for fiscal years (FY) 1954 and 1955. Legislation in 1954 authorized an additional $175 million annually for FY 1956 and 1957. It was under the leadership of President Dwight D. Eisenhower that the question of how to fund the Interstate System was resolved with the enactment of the Federal-Aid Highway Act of 1956. This Act served as a catalyst for the System's development and, ultimately, its completion.
Title I of the 1956 Act increased the System's length to 41,000 miles. It also called for nationwide standards for design of the System, authorized an accelerated program, established a new method for apportioning funds among the States, set the Federal Government's share of project cost at 90 percent and added the words "and Defense" to the name of the System, thereby changing the name to The National System of Interstate and Defense Highways.
Title II of the Act, entitled the Highway Revenue Act of 1956, created the Highway Trust Fund as a dedicated funding source for the Interstate System's continued construction. Revenue from the Federal gas and other motor-vehicle user taxes was credited to the Highway Trust Fund to pay the Federal share of Interstate and all other Federal-aid highway projects. In this way, the Act guaranteed construction of all segments of the System on a "pay-as-you-go" basis as revenue flowed into the Highway Trust Fund. This ensured that funds needed to construct the System would not create a deficit in the U.S. Treasury's General Fund, thus satisfying one of President Eisenhower's primary requirements that the program be self-financing.
The Federal-Aid Highway Act of 1956 called for uniform geometric and construction standards for the Interstate System. The standards, which have been revised periodically over the years, were developed by the State transportation departments, through the American Association of State Highway and Transportation Officials (AASHTO), and adopted by the FHWA. The standards include a minimum of four 12-foot wide travel lanes, a minimum shoulder width of 10 feet, full control of access, and design speeds of 50 to 70 miles per hour (depending on the type of terrain). Initially, the design had to be adequate to meet the traffic volumes expected in 1975. Later, the requirement was changed to a more general 20-year design period rather than for a specific year to allow for evolution of the System. The design standards have been codified in Section 109(b), 23 U.S.C.
The Federal-Aid Highway Act of 1968 authorized the System's expansion to 42,500 miles. An amendment sponsored by U.S. Representatives James Howard and William Cramer authorized an additional 200 miles for modification or revision of the basic System. The mileage authorized under the Howard-Cramer Amendment was increased eventually to 500 miles under the Federal-Aid Highway Act of 1973.
The Surface Transportation Assistance Act of 1978 provided full Interstate Construction funding for all routes designated under previous System adjustments. Another provision of this Act prohibited the use of Interstate Construction (IC) funds for the construction of any new miles designated after passage of the Act. A total of 42,795 miles had been designated for development with IC funds before this measure was enacted.
The FHWA may, at the request of a State or States, designate sections of the National Highway System (NHS) as Interstate Highway under Section 103(c)(4)(A), Title 23, United States Code (23 U.S.C.). The proposed section must:
Although Section 103(c)(4)(A) segments look like any other Interstate highway, they are not eligible for development with IC funds. In all, the FHWA has approved 3,761.92 miles of highways in the contiguous 48 States, District of Columbia, and Hawaii as Section 103(c)(4)(A) additions to the Interstate System (including additions under former Section 139(a)).
Also added to the Interstate System under Section 103(c)(4)(A) are highways in Alaska and Puerto Rico for a total of 1,331.99 miles (including additions under former Section 139(c)). Alaska and Puerto Rico are exempt from the design standards of Section 109(b). Section 103(c)(1)(B)(ii), 23 U.S.C., states: "Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway."
The FHWA may also, at the request of a State or States, add highways to the Interstate System that are designated as National Highway System (NHS) high priority corridors and future parts of the Interstate System in Section 1105 of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). The proposed section must:
Four future Interstate corridors were initially designated by the National Highway System Designation Act of 1995. Modifications and an additional 16 future Interstate corridors were designated by subsequent laws.
Future Interstate route numbers for five of the corridors are also specified by these Acts. The corridors are generally described as:
Construction and improvement of these corridors are eligible for funds under the NHS program and the Surface Transportation Program. In addition, Highway Bridge Program funds may be used to rehabilitate deficient bridges on these routes. The corridors are not eligible for IC funds.
As of December 31, 2016, 1,387.07 miles of Section 1105 future Interstate corridors in 11 states have been upgraded to Interstate standards and added to the Interstate System.
Today's Interstate System, as of December 31, 2016, is comprised of the designated mileage developed with IC funds and additions under Section 103(c)(4)(A), 23 USC and Section 1105, ISTEA, for a total of 49,072.26 miles. It serves the 48 contiguous States, Alaska, Hawaii, the District of Columbia and Puerto Rico. The Interstate routes in the 48 contiguous States and the District of Columbia are designated with a prefix "I" followed by a number (1 to 3 digits). Alaska has four routes, designated A1, A2, A3 and A4, Hawaii has four routes, designated H-1, H-2, H-3 and H-201, and Puerto Rico has three routes designated PRI-1, PRI-2 and PRI-3.
As of December 31, 2016, 42,787 miles, (more than 99.9 percent), of the 42,793 Interstate miles designated under former Section 103(e) were open to traffic. The segments open to traffic include 40,378 miles that are complete or essentially complete. The other 2,409 miles include 53 miles requiring major improvements to bring them to full Interstate standards, 124 miles currently under improvement or still requiring additional minor work to complete initial construction and 2,233 miles of toll roads, which, in general, were built without Federal funding. To date, 47 States have opened their total designated Interstate mileage. Only about 6 miles are not open to traffic: (1) 2.4 miles of I-90 in Massachusetts, (2) 1.7 miles of I-670 in Ohio and (3) 1.5 miles of I-95 in Pennsylvania.
Completion of the $129-billion designated mileage (42,793 miles) in the Interstate System was a cooperative Federal-State undertaking. Each State transportation department managed its own Interstate program for location, design, right-of-way acquisition, and construction of the designated mileage. The FHWA's role was one of review and approval of the projects to ensure compliance with Federal requirements. Ownership of the Interstate routes and the responsibility for their operation and maintenance, rest with each State.
Initially, all Interstate maintenance responsibility was placed on the States. However, as the System aged, a separate federally funded program, committed to preserving the System, was enacted in 1976 called the Interstate 3R (resurfacing, restoration & rehabilitation) Program. In 1981 the Interstate 3R program was expanded to a 4R program with the addition of reconstruction as an eligible item. The current program, enacted in 1991 and continued by TEA-21 is called the Interstate Maintenance Program which provides funds to the States for maintaining an acceptable level of service on the System. However, Interstate routes added under Section 103(c)(4)(A) after TEA-21 will not be eligible for the Interstate Maintenance funds.
Beginning in the 1956 Act, the System was called The National System of Interstate and Defense Highways. In honor of President Eisenhower, who helped accelerate the Interstate Construction Program, Public Law 101-427 was passed which changed the name of the System to "The Dwight D. Eisenhower System of Interstate and Defense Highways." This occurred on October 15, 1990, during the celebration of the 100th anniversary of President Eisenhower's birth. The Intermodal Surface Transportation Efficiency Act of 1991 modified the name to "The Dwight D. Eisenhower National System of Interstate and Defense Highways" and this definition is codified in Sections 101(a)(13) and 103(c)(1)(A), 23 U.S.C.
AASHTO developed the procedure for numbering the Interstate routes, with Bureau of Public Roads (BPR) concurrence, in 1957. The BPR is the predecessor of the FHWA. The Interstate route marker is a red, white, and blue shield, carrying the word "Interstate, " the State name, and the route number. Major Interstate routes are designated by one- or two-digit numbers. Routes running north and south are assigned odd numbers, while east-west routes are assigned even numbers. For north-south routes, the lowest numbers begin in the west, while the lowest numbered east-west routes are in the south. Thus, Interstate Route 5 (I-5) runs along the West Coast, while I-10 lies along the southern border.
In a few cases, a major route has two parallel or diverging branches. In those cases, each branch is given the designation of the main route, followed by a letter indicating a cardinal direction of travel (east, west, etc.). In Texas, for example, I-35 splits at Hillsboro, with I-35E going through Dallas, while I-35W goes through Fort Worth. The two branches merge at Denton to reform the main route, I-35.
The major route numbers are routed through urban areas on the path of the major traffic stream. Generally, this major traffic stream will be the shortest and most direct line of travel. Connecting routes and full or partial circumferential beltways around and within urban areas carry a three-digit number. These routes are designated with the number of the main route and an even-numbered prefix. Supplemental radial and spur routes, connecting with the main route at one end, also carry a three-digit number, using the number of the main route with an odd-numbered prefix.
To avoid duplication within a State, a progression of prefixes is used for the three-digit numbers. For example, if I-80 runs through three cities in a State, circumferential routes around these cities would be numbered I-280, I-480, and I-680. The same system would be used for spur routes into the three cities, with routes being numbered I-180, I-380, and I-580. This system is not carried across State lines. As a result, two cities in different States along I-80 may each have circumferential beltways numbered I-280 or spur routes numbered I-180.
The sketch below indicates this pattern.
The States typically use one of two methods of numbering the Interstate interchanges:
In the contiguous 48 States and the District of Columbia, 62 main one- or two-digit numbered routes have been assigned. Of these, 27 are in a primarily east-west alignment and therefore carry an even number. Another 35 routes are odd-numbered because of their primarily north-south alignment. Although 261 auxiliary circumferential, spur, and radial routes are designated, only 151 three-digit numbers have been assigned. This is because three-digit numbers can be used in more than one State.The five longest Interstate routes, each more than 2,000 miles, are east-west routes. These are:
Among the 2-digit Interstate routes, the five shortest are:
The shortest Interstate route segment is I-95 in the District of Columbia which is 0.11 mile long.
The Interstate System connects 46 of the 50 State capitals, as well as the Nation's Capital, Washington, D.C. The four State capitals not directly served by the Interstate System are Juneau, Alaska; Dover, Delaware; Jefferson City, Missouri; and Pierre, South Dakota.
The oldest Interstate segments actually predate the establishment of the Interstate system. Early examples include a portion of the Grand Central Parkway in Queens, New York, which was opened to traffic in July 1936, and later was incorporated into the Interstate System as I-278. The Pennsylvania Turnpike between Irwin (southeast of Pittsburgh) and Carlisle (west of Harrisburg) was officially opened in October 1940, and is now designated as I-76 and I-70. Other freeways and toll roads were incorporated into the System under the 1956 Act, as an alternative to building new competing Interstate routes.
The route log for the Interstate System presented in this booklet was prepared to provide a simple way of locating routes by number and determining which routes serve each State and its larger cities. It is not intended to serve as a touring guide. The booklet includes the following:
Main Route Log: This log lists the one- or two-digit numbered main routes, arranged numerically. The total length of each route is shown. The net length is provided for routes that partially overlap another route and the duplicated length is assigned to the latter. The list also shows additional mileage designated under the Howard-Cramer Amendment, Section 103(c)(4)(A), 23 U.S.C. and Section 1105(e)(5)(A) of ISTEA as amended. The principal urban areas, with populations of 5,000+, served by the route are listed for each State.
Auxiliary Route Log: This log lists the three-digit numbered circumferential, belt, or loop and spur routes principally serving urban areas. The routes are listed numerically, along with the State, the mileage, and the principal city served. As explained previously, the same number may be used in several States, but cannot be duplicated within a State's borders.
Routes per State: This log lists the States alphabetically and shows all the Interstate routes for each State and their totals.
List of Major Cities Served: This list shows all the cities of more than 50,000 population (1990 Census and latest available estimates) served by the Interstate System. States are shown alphabetically, with the cities listed alphabetically within each State. For each city, the main and auxiliary routes serving that city are listed.
The routes and route numbers shown are all routes on the Interstate System As of December 31, 2016. The mileage is from the official records of the System as reported by the States and reviewed by the Federal Highway Administration.
A bridge over the Zumbro River in historic Mantorville, Minnesota.